Speaker
Description
Gravity fingering is a hallmark instability during infiltration into dry porous media, where small perturbations in the wetting front amplify into preferential flow paths that strongly influence water and solute transport in soils. Despite decades of numerical and laboratory investigations, a persistent challenge has been directly linking pore-scale invasion mechanisms to the macroscopic emergence and evolution of gravity fingers. Conventional three-dimensional experiments obscure pore-scale dynamics, while pore-scale studies typically lack the spatial extent required to capture multi-finger behavior.
In this work, we investigate gravity-driven infiltration using high-resolution optical imaging in quasi-two-dimensional, macroscale microfluidic flow cells. The devices consist of micron-scale cylindrical posts that mimic soil pore geometry, arranged within centimeter-scale domains that allow multiple gravity fingers to form and interact. This unique platform enables real-time visualization of pore-scale wetting, meniscus dynamics, and local instabilities, while simultaneously tracking the growth, spacing, and competition of gravity fingers at the macroscopic scale.
Our experiments reveal how pore-scale invasion processes, including local capillary thresholds, interface curvature, and heterogeneity-induced perturbations, collectively govern finger initiation and selection. By directly observing the transition from a nominally uniform wetting front to discrete gravity fingers, we establish a mechanistic connection between microscale physics and emergent macroscopic flow patterns. These results provide new experimental constraints for continuum and pore-scale models of unsaturated flow and offer a physically transparent framework for understanding preferential flow in soils and other porous materials.
| Country | Canada |
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